Field of the Invention
The present invention relates to a method of manufacturing an optical fiber, an optical fiber manufacturing apparatus, and a control apparatus that controls the manufacturing apparatus.
Description of the Related Art
Generally, in manufacture of an optical fiber, a method is employed which vertically and downwardly draws an optical fiber from an optical fiber preform along a linear pathway.
The overall height of the system thereof is limited and becomes a factor that affects the productivity of the manufacturing method. Because the height of the system becomes a main factor that limits the productivity, it is necessary to ensure the distance of a bare optical fiber in the system which is required to sufficiently cool the bare optical fiber obtained by drawing an optical fiber preform.
The above-described limitation can be eased by construction of new facilities such as new buildings; however, a huge cost is necessary in order to ease the limitation, if improvement in productivity is required in the future, it will be necessary to construct new facilities at great expense.
As a method of easing the limitation, a method of using a direction changing device that includes a noncontact retention mechanism and changes the direction in which a drawn fiber is drawn is known.
This noncontact retention mechanism is a mechanism that contactlessly retains an object by using a pressure of fluid such as air, and a direction changer that is provided with this mechanism can change the direction, in which a bare optical fiber (bare fiber) is drawn, without being in contact with the bare optical fiber.
By using this direction changer, the direction of a bare optical fiber which is fiber-drawn a optical fiber preform along a first pathway can be changed into a direction along a second pathway (for example, refer to Japanese Patent No. 5571958 and Japanese Unexamined Patent Application, First Publication No. S62-003037).
Japanese Patent No. 5571958 discloses a method of manufacturing an optical fiber, which uses a direction changing device that changes the direction of a drawn fiber. The instrument has a groove into which an optical fiber is to be introduced, and the groove has an opening firmed therein. In this method, a gas that is introduced into the instrument is discharged through one flow inlet port, and a direction of an optical fiber is changed in a state where the optical fiber floats due to the pressure of the gas.
Japanese Unexamined Patent Application, First Publication No. S62-003037 discloses a direction changer, the direction changer has a guide groove that guides a bare optical fiber into, and gas outlet nozzles are formed on the bottom surface and both side surfaces of the guide groove (refer to Example and FIGS. 3 and 4). In this manufacturing method using the direction changer, a direction of an optical fiber is changed due to the pressure of the gas blown from four outlet nozzles in a state where the optical fiber floats.
The amount of flotation of the bare optical fiber is determined by the balance between: a pressure of the gas blown in a groove; and a drawing tension applied to a bare optical fiber. Therefore, in the case where the gas pressure and the drawing tension are constant, the amount of flotation of the bare optical fiber is also constant, and a stable fiber drawing is thereby possible.
However, in an actual manufacturing process, a drawing tension varies due to variation in an outer diameter of an optical fiber preform, variation in the drawing speed of a bare optical fiber, or the like, as a result, the amount of flotation of the bare optical fiber varies in some cases.
In the case where the drawing tension is low, as the amount of flotation the bare optical fiber increases, a stability in a flotation state is degraded, and there is a concern that bare optical fiber is in contact with the inner surface of the groove of the direction changing device. In the case where the bare optical fiber comes into contact with the direction changing device, the bare optical fiber is damaged, and there is a possibility that the strength of the bare optical fiber is degraded. On the other hand, in the case where the drawing tension is high, as the amount of flotation of the bare optical fiber decreases, there is a concern that bare optical fiber is in contact with the inner surface of the groove of the direction changing device. In the case where the bare optical fiber comes into contact with the direction changing device, the bare optical fiber is damaged, and there is a possibility that the strength of the bare optical fiber is degraded.
Furthermore, in both cases where the drawing tension is high and low, as the position at which the bare optical fiber is introduced into a coating unit varies due to variation in the flotation position, and there is a concern that deviation thickness of the coating occurs.